Peter - I have an EPIRB on my boat. If I had to do over again I would look into the PLBs. A lot of the guys I know have bought and use the PLBs (Personal Locator Beacons).
These are registered to YOU not the boat so you can carry it with you out on anyone's boat.
One of the drawbacks to the PLB are the transmit time when activated. They are smaller and have less battery capacity.
Here is a little info on them -
PLBs
Most are using the ACR - this unit -
ACR aquafix